Iranian Journal of Materials Science and Engineering

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In this study different volume fractions of SiC particles of various sizes were introduced into the semisolid A356 aluminum alloy by a mechanical stirrer. Then the slurry was poured into a permanent die of certain dimensions either when the metal alloy was partially solid (semisolid-semisolid or SS route) or after reheating to above the liquidus temperature of the alloy (semisolid-liquid or SL route). Both the SS and SL composite samples were solution-treated at 520°C for 8 hours followed by quenching in water at room temperature. Microstructural characterization studies have been conducted on both the SL and SS samples to quantify the effects of the size andcontent of the SiC particles as well as the solutionizing treatment on the morphology and size ofthe eutectic silicon particles and the matrix grain (globule) size. The results were rationalized in terms of the different nucleation, fragmentation, spherodization and coarsening events, which had taken place during the processing of these composites. Finally the impact of these microstructural features in improving the wear properties of the composites has been discussed.

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ZnS : Cu phosphors were prepared by using laboratory grade chemicals through coprecipitating Cu along with ZnS using H2S and thiourea. Photo- and electroluminescence studies indicate that these phosphors have better emission characteristics compared to the phosphors in which activator is externally added. Phosphors with luminescence at ~530nrn were prepared. The difference between the characteristic properties of the samples seems to be due to formation of nanoparticles during the preparation of the samples by different methods.

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Fracture behavior of a 7075 aluminium alloy reinforced with 15 Vol%. SiC particles was studied after T6 and annealing heat treatments under uniaxial tensile loading at room temperature. The scanning electron microscopy of fractured surfaces and EDS analysis showed:, that fracture mechanism changed from due mainly to fractured particle in T6 condition to interface decohesion in samples in annealed state. Different fracture mechanisms in annealed and T6 conditions can be ascribed mainly to the significant difference in the stress concentration levels around the particles. In T6 condition, very high local stress sufficient to cause fracture of particle can be generated during loading, while the presence of large precipitates at the particle/matrix interface produced interface decohesion leading to final fracture in the annealed state.

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In wire arc spraying, the atomizing air pressure and applied nozzle system are important factors influencing particles characteristics and coating quality. The aim of this paper is to study how the characteristics of particles such as size, velocity and temperature are influenced by the operating conditions in wire arc spray. For that, three types of wires are tested: solid wire of stainless steel 316L, cored wires 97MXC and 98MXC. Arc spray gun is an Arc Jet 9000 manufactured by TAFA. For each condition, the particles temperature and particles velocity are measured using an imaging CCD camera, Spray Watch (Oseir Ltd). Particles size distributions are determined with a laser grain meter. The morphology and composition of particles were evaluated with SEM, EDX and X-Ray diffraction. Results induce important modifications in the particles size distributions and particles velocity. A small diameter nozzle and high atomizing air pressure resulted in a reduction in particles size distributions and an increase in particles velocity.

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Abstract: Static recrystallization (SRX) behavior of a composite based 7075 Aluminum alloy reinforced with SiC particles was studied during annealing the deformed samples at high temperatures. The results showed an absence of SRX in the samples annealed after hot working at the same deformation temperature, however, a rise in annealing temperature of 100-1500 􀁱C above that the deformation temperature led to full recrystallization. This can be ascribed to the relatively moderate dynamic recovery and the presence of dispersions which stabilize the substructure. Particle stimulated nucleation (PSN) had a significant effect on the grain size in deformed samples at low temperature, but no PSN was observed in samples strained at high temperatures. The possible cause might be that at high temperature the dislocations can be annihilated by climb process around the particles together with the absence of deformation zone for nucleating the recrystallization.

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Abstract: Problems such as the difficulty of the selection of processing parameters and the large quantity of experimental work exist in the morphological evolutions of Semisolid Metal (SSM) processing. In order to deal with these existing problems, and to identify the effect of the processing parameters, (i.e. shearing rate-time-temperature) combinations on particle size and shape factor, based on experimental investigation, the Artificial Neural Network (ANN) was applied to predict particle size and shape factor SSM processed Aluminum A.356.0 alloy. The results clearly demonstrated that, the ANN with 2 hidden layers and topology (4, 2) can predict the shape factor and the particle size with high accuracy of 94%.The sensivity analysis also revealed that shear rate and solid fraction had the largest effect on shape factor and particle size, respectively. The shear rate had a reverse effect on particle size.

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Abstract: Thermal fatigue is a stochastic process often showing considerable scatter even in controlled environments. Due to complexity of thermal fatigue, there is no a complete analytical solution for predicting the effect of this property on the life of various components, subjected to severe thermal fluctuations. Among these components, one can mention car cylinder, cylinder head and piston which bear damages due to thermal fatigue. All these components are usually produced by casting techniques. In order to comprehend and compare the thermal fatigue resistance of cast Al alloys 356 and 413, this research was designed and performed. For this purpose, several samples in the form of disc were cast from the two alloys in sand mould. The microstructures of the cast samples were studied by light microscopy in order to choose the samples with the least amounts of defects for thermal fatigue tests. The results of thermal fatigue tests showed that the nucleation of microcracks in Al-356 alloy occurred at shorter time relative to those occurred in Al- 413 alloy under the same test conditions. In addition, the density of micro-cracks in Al-356 alloy was more than that of Al-413 alloy. The results of fractography on 356 alloy indicated that the cracks were generally nucleated from inter-dendritic shrinkage porosities and occasionally from the interface of silicon particles with the matrix. The growth of these micro cracks was along the dendrite arms. Fractography of 413 alloy fracture surfaces showed that nucleation of microcracks was often associated with silicon particles.

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Abstract: Nanoparticles exhibit a high reactivity and strong tendency towards agglomeration. In this study, aluminum oxide (alumina) nanoparticles were characterized by gas adsorption (BET), transmition electron microscopy (TEM) and photon correlation spectroscopy (PCS) techniques to assess the agglomeration of the particles. There is a good correlation between the BET and TEM measurements but PCS was larger in the mean and median size and with a degree of agglomerates being detected. Some agglomeration was evident, but most of the particles existed as discrete objects as observed in the (HR) TEM images which were in good agreement with the agglomeration factor.

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Abstract: Nano- size alumina particles have been synthesized by mechanical activation of a dry powder mixture of AlCl3 and CaO. Mechanical milling of the above raw materials with the conditions adopted in this study resulted in the formation of a mixture consisting of crystalline CaO and amorphous aluminum chlorides phases. There was no sign of chemical reaction occurring during milling stage as evidenced by x-ray diffraction studies. Subsequent heat treatment of the milled powder at 350ºC resulted in the occurrence of displacement reaction and the formation of Al2O3 particles within a water soluble CaCl2 matrix. The effect of higher temperature calcinations on the phase development in this powder mixture was followed by X-ray diffraction (XRD) analysis and scanning electron microscope ( SEM). Differential thermal analysis (DTA) was used to compare the thermal behavior between the milled and unmilled powders. Perhaps the most important result in this study was the observation of á-Al2O3 phase at a very low temperature of 500ºC.

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Abstract:In this study, an effort has been made to determine the influence of rotational speed of tool on themicrostructure and hardness values of friction stir welded 2024-T851 aluminum alloy. The microstructure of stir zonein the joints has been investigated. It was found that the particles such as Al6(CuFeMn) particles are broken up duringfriction stir welding, and the degree of break up of these particles in the stir zone increases with increasing rotationalspeed. Since the break up of these particles and the recrystallization of new grains happen simultaneously, the brokenparticles would be placed in the grain boundaries. Moreover, the hardness value in the stir zone increases withincreasing rotational speed

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Abstracts:

nanoparticles. All the extracts were used separately for the synthesis of gold nanoparticles through the reduction of

aqueous AuCl

gold ions to gold nanoparticles. The ethanol extract of black tea and its tannin free ethanol extract produced gold

nanoparticles in the size ranges of 2.5-27.5 nm and 1.25-17.5 nm with an average size of 10 nm and 3 nm, respectively.

The prepared colloid gold nanoparticles, using the ethanol extract of black tea, did not show the appropriate stability

during storage time (24 hours) at 4

showed no particle aggregation during short and long storage times at the same conditions. To the best of our

knowledge, this is the first report on the rapid synthesis of gold nanoparticles using ethanol extract of black tea and

its tannin free fraction.

In this research the ethanol extract of black tea and its tannin free fraction used for green synthesis of gold4¯. Transmission electron microscopy and visible absorption spectroscopy confirmed the reduction ofoC. In contrast, gold colloids, which were synthesized by a tannin free fraction

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Abstract: Most properties of nanoparticles are size-dependent. In fact, the novel properties of nanoaprticles do not prevail until the size has been reduced to the nanometer scale. The particle size and size distribution of alumina nanoparticle, as a critical properties, have been determined by transmission electron microscopy (TEM), photon correlation spectroscopy (PCS), surface area analysis (BET) and x-ray diffraction peak broadening analysis. The particle size was found to be in the range of 5-95nm. Cumulative percentage frequency plot of the data extracted form TEM images indicates that particle size distribution obeys the log-normal function. The TEM images also reveal that particles are spherical in shape and loosely agglomerated. Comparing of the XRD and TEM results shows that the particles are single-crystal. The HRTEM images also verify that the particles have a single-crystal nature. In comparison, there is a good correlation between the BET, XRD and TEM measurements other than PCS that is sensitive to the presence of the agglomerates.

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Ultraviolet–Visible (UV–Vis) spectroscopy was used, in the current investigation, to explore the dispersion and stability of titania nanoparticles in an aqueous media with different types of dispersants. Hydrochloric and nitric acids as well as ammonia were used to determine the stability of the suspension in the acidic region (pH=2.5) and basic area (pH=9.5), respectively. In addition, for measuring sustainability of suspension and creating steric, and electrosteric repulsive forces, ethylene glycol and ethylene glycol plus ammonia were employed, respectively. UV–V is
spectrometry was applied to realize the effect of nano titania concentrations and different types of dispersants of samples containing different amounts of nano titania and different types of dispersants on stability of TiO2-containing suspensions. In addition, the stability of dispersion could be evaluated in colloidal mixtures containing ethylene glycol plus ammonia. It was demonstrated that the mixtures containing ethylene glycol plus ammonia were stable over a period of 4 days. To support the UV–Vis results, other techniques such as atomic force microscopy (AFM) and scanning electron microscopy (SEM) were employed to study the degree of agglomeration of titania nanoparticles in terms ofmorphology and size.

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Yellow-colored nitrogen doped TiO2 photocatalyst and a pure TiO2 powder were synthesized via sol-gel method using TiCl4 and urea as raw materials. However, the synthesis procedure for nitrogen doped TiO2 was catalyzed by acid that dialed with controlled precipitation and slow nucleation. According to XRD analysis, the nitrogen doped TiO2 consisted of anatase phase of titania which was a significant achievement regarding its possible photocatalytic applications. The band gaps of nitrogen doped TiO2 and pure TiO2 were estimated from UV-Vis spectroscopy data to be 2.8 and 3.3 ev, respectively. Photocatalytic properties of the nitrogen doped TiO2 nanocatalyst and pure TiO2 were compared for degradation of crystal violet dye in visible light irradiation. In comparison to pure TiO2, nitrogen doped TiO2 showed superior photocatalytic efficiency towards the dye.

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Abstract:In recent years, there have been many attempts to improve the properties of dental amalgam. The aim of the present investigation was fabrication and characterization of dental amalgams containing TiO2 nanoparticles and evaluation of their compressive strength, antibacterial and corrosion behavior. In this experimental research, TiO2 nanoparticles (TiO2 NPs) were added to reference amalgam alloy powder and then, dental amalgam was prepared. In order to investigate the effect of TiO2 NPs on properties of dental amalgam, 0, 0.5, 1, 2 and 3 wt. % of TiO2 NPs were added to amalgam alloy powder and the prepared composite powder was triturated by a given percent of mercury. Xray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy-Dispersive Spectroscopy (EDS) techniques were used to characterize the prepared specimens. Potentiodynamic polarization corrosion tests were performed in the Normal Saline (0.9 wt. % NaCl) Solutions as electrolytes at 37°C. The results showed that the corrosion behavior of the dental amalgam with 0.5 or 1 wt. % TiO2 NPs is similar to the corrosion behavior of the reference amalgam, while with increasing the weight percent of TiO2 NPs, the corrosion rate increases. Also, the results of this investigation indicated that adding TiO2 NPs in amounts of up to 1 wt. % to amalgam alloy powder improve compressive strength of dental amalgam and has no destructive influence on its corrosion behavior. As well as, according to antibacterial results, TiO2 NPs can increase the biocompatibility and antibacterial activity of dental amalgam. The results of present study suggest that amalgam/ TiO2 NPs nanocomposite with 1% of TiO2 NPs could be regarded as a biocompatible and bioactive dental material that provide better characters for dental applications.

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Accumulative roll-bonding process (ARB) is an important severe plastic deformation technique for production of the ultrafine grained, nanostructured and nanocomposite materials in the form of plates and sheets. In the present work, this process used for manufacturing Al/SiO 2 nanocomposites by using Aluminum 1050 alloy sheets and nano sized SiO 2 particles, at ambient temperature. After 8 cycles of ARB process, the tribological properties and wear resistance of produced nanocomposites were investigated. The wear tests by abrasion were performed in a pinon-disc tribometer. Results show that by increasing ARB cycles and the amount of nano powders, the friction coefficient of produced nanocomposites decreases.

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Silver nanoparticles are being given considerable attention because of their interesting properties and potential applications. One such exploitable use is as the major constituent of conductive inks and pastes used for printing various electronic components. This paper presents a novel direct-writing process for fabrication of the first deposited silver nanoparticles (AgNPs) (50-200nm) electrode via a thermal inkjet printer. In this method, AgNPs were chemically deposited by ejection of ascorbic acid and silver nitrate solutions onto different substrates such as paper and textile fabrics. Silver deposited patterns were used as electrodes in different electrochemical experiments and their morphology was also investigated in SEM observations. The highest conductivity of deposited electrodes obtained on paper as the substrate was found to be around 5.54x105 S/m. Inkjet fabricated electrodes exhibited acceptable electrochemical behavior in experiments designed for measuring the concentration of hydrogen peroxide as a fundamental procedure for early determination of glucose. This novel inkjet silver deposition technique is introduced to be considered as a promising method for ultimate single step fabrication of different electrochemical bio-sensors.

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High energetic aluminum nanoparticles are mainly used as additive in solid rocket propellants. However, fabrication of these aluminized energetic materials is associated with decreasing the burning rate of propellants due to problems such as oxidation and agglomeration of nanoparticles. In this study, to improve combustion performance of aluminum nanoparticles, coating by metallic Ni shell was studied. Nickel coating of aluminum nanoparticles was performed through electroless deposition (ED) subsequently, morphology and chemical composition of Ni-coated nanoparticles were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). These studies show that a uniform Ni layer with a thickness of 10nm is coated on the surface of Al nanoparticles. Thermal analysis of uncoated and Ni-coated aluminum nanoparticles was done using differential thermal analysis (DTA) and thermo gravimetric analysis (TGA). The results of thermal analysis indicate that, coating the aluminum particles by Ni, leads to improvement in combustion performance of aluminum nanoparticles through decreasing critical ignition temperature, ignition delay time of the nanoparticles and promoting the ignition by exothermic chemical reactions between Al and Ni

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Aluminium base alloy (Al-Cu-Si) was reinforced with silicon carbide (SiC) particles, in various percentage compositions from 0-20 wt%. Silicon carbide particle size of 20µm was selected. The molten slurry of SiC reinforced base aluminium metal was casted through green and dry sand casting methods and solidification process was carried out under ambient conditions. A selected population of total casted samples were subjected to T6 heat treatment process, followed by evaluation of mechanical properties of hardness, tensile strength and impact loading. The micro sized SiC particles were preheated up to 300C prior pouring into the melted metal, for subsequent removal of residual gases and moisture content. A continuous manual stirring method was used for homogenous distribution of reinforced particle in molten slurry. The experimental results revealed that the highest parameters of hardness, impact energy and tensile strength were achieved in the T6 heat treated specimens having highest percentage composition (20%) of Silicon Carbide (SiC) particles

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A homogenous TiO₂ / multi-walled carbon nanotubes(MWCNTs) composite film were prepared by electrophoretic co-deposition from organic suspension on a stainless steel substrate.  In this study, MWCNTs was incorporated to the coating because of their long structure and their capability to be functionalized by different inorganic groups on the surface. FTIR spectroscopy showed the existence of carboxylic groups on the modified carbon nanotubes surface. The effect of applied electrical fields, deposition time and concentration of nanoparticulates on coatings morphology were investigated by scanning electron microscopy. It was found that combination of MWCNTs within TiO₂ matrix eliminating micro cracks presented on TiO₂ coating. Also, by increasing the deposition voltages, micro cracks were increased. SEM observation of the coatings revealed that TiO₂/multi-walled carbon nanotubes coatings produced from optimized electric field was uniform and had good adhesive to the substrate.